1. Field of the Invention
The present invention relates to a decorated resin molded article and a method for producing the decorated resin molded article. More particularly, the invention relates to a decorated resin molded article having a metallic decoration applied on a design surface of a substrate constituted by a resin molded article, and to a method for advantageously producing the decorated resin molded article.
2. Description of the Related Art
As one type of decorated resin molded articles, there are known decorated resin molded articles each provided with a so-called metallic decoration in which a metallic surface in appearance is provided by forming, for example, a metallic coating film or a metal plating film on the design surface of a substrate constituted by a resin molded article (for example, see JP-A-2004-300566). The decorated resin molded articles have a lighter weight, better moldability, and higher processability than real metal products and do not require any rust prevention processing. Thus, they have been broadly used as surface skin materials, parts, or the like of various products and items such as automobile interior parts, furniture, building materials, home electric appliances, and mobile electronic apparatuses.
However, among the above conventional decorated resin molded articles, articles having a decoration provided by forming the metallic coating film on the design surface of the substrate tend to have an uneven appearance resulted from a difference of the amount of reflective light due to thickness irregularity of the metallic coating film, or tend to have a coating defect such as a “wave” or an “orange peel”. This causes a deterioration of designability of a surface of the coating film, and ultimately, of the design surface decorated by the coating film. Furthermore, the articles having a decoration provided by forming the metal plating film on the design surface of the substrate have a problem that a harmful waste liquid is generated during a process for forming the metal plating film.
In the conventional decorated resin molded articles, the metallic coating film or the metal plating film is generally formed to have a relatively large thickness ranging from a few tens to a few hundreds μm on the design surface of the substrate. Thus, the shapes of corners and edges of the design surface become rounded, thereby inevitably losing sharp appearance that is particular to metal. Consequently, it is extremely difficult to sufficiently obtain a metal texture in appearance. Hereinafter, the metal texture is referred to as “realistic metal texture”.
Under such circumstances, there is also proposed a decorated resin molded article having a metallic decoration provided by forming a metal film on a design surface of a substrate by a physical vapor deposition method such as sputtering or evaporation (for example, see U.S. Pat. No. 6,637,920 and JP-A-2004-174921). In those decorated resin molded articles, the metal film has an extremely thin and uniform thickness as compared to the metallic coating film, the metal plating film, and the like. In addition, no harmful waste liquid is generated during the formation process of the metal film. Therefore, the molded articles are free from problems such as the deterioration of designability and the safety issue during the production process, which inherently exist in the above conventional articles decorated by the metallic coating film or the metal plating film.
In the above decorated resin molded articles, generally, a topcoat layer (a protective layer) that has a high adhesiveness (cohesion) to metal and that is made of a transparent coating film is laminated on the metal film so as to protect the metal film having the extremely thin thickness. In addition, between the metal film and the design surface is provided an undercoat layer (a base layer) formed of a predetermined coating film to increase the adhesiveness of the metal film to the design surface. Furthermore, the undercoat layer prevents the design surface of the substrate from being eroded by a component part (for example, an organic solvent such as thinner) that is contained in the topcoat layer and that penetrates through the metal film. Thereby, durability of the decorated resin molded articles can be improved.
However, in the above-described conventional decorated resin molded articles that includes the undercoat layer, the metal film, and the topcoat layer which are laminated sequentially from a bottom side on the design surface, the undercoat layer is constituted by a coating film formed of a predetermined coating material which is applied on the design surface, and the undercoat layer has a thickness of 10 μm or more. Thus, also in the conventional decorated resin molded articles having the above-described structure, although the metal film has the sufficiently thin thickness, the corners and the edges of the design surface are made to have round shapes by the undercoat layer having the large thickness formed between the metal film and the design surface. Thereby, the molded articles inevitably appear less sharp and lack a somewhat realistic metal texture like the conventional decorated resin molded articles that have the decorations provided by the metallic coating film or the metal plating film as already described.
There is also known a decorated resin molded article in which a decoration is provided on a design surface by using a metal film formed by sputtering, and no undercoat layer is formed between the metal film and the design surface (for example, see U.S. Pat. No. 7,086,766). With the structure, it is expected that the corners and the edges of the design surface are sharpen and thus the “realistic metal texture” can be sufficiently represented. However, omission of the undercoat layer causes a reduction in the adhesiveness of the metal film to the design surface and also makes it difficult to prevent the erosion of the design surface of the substrate caused by the component part of the topcoat layer penetrated through the metal film. As a result, for example, the metal film is easily separated from the design surface, which result in reduction in the durability of the decorated resin molded article.
Along with the undercoat layer, the topcoat layer may also be omitted. However, the metal film cannot be protected without the topcoat layer, and it becomes difficult to prevent abrasion, separation, damage, or the like of the metal film, which are caused by contact of the metal film with another constituent member. In addition, it becomes difficult to secure a durability of the metal film against various chemicals or the like. Accordingly, also in this case, the durability of the decorated resin molded article is extremely deteriorated.